Recycled Concrete Beams Research Articles

Fracture analysis of seawater sea-sand recycled aggregate concrete beams: Experimental study and analytical model

Seawater sea-sand recycled aggregate concrete (SSRAC) has garnered significant attention from engineers involved in various coastal engineering projects. Fracture constitutes one of the primary failure modes of SSRAC, and the accurate analysis of its fracture behavior is crucial for application. In this present study, SSRAC with 50% aggregate replacement was subjected to three-point bending tests to evaluate its fracture performance. Specific methodologies for calculating SSRAC fracture toughness were introduced, taking into account the effects of material microstructures and specimen boundaries. By comparing the fracture properties of SSRAC specimens with varying initial notch lengths, the size effect was addressed by using established methods, resulting in a constant fracture toughness value. Furthermore, the methods for analyzing the fracture of un-notched specimens were developed, considering fracture path analysis and the influence of internal defects. Notably, this research demonstrated that small specimens and established methodologies efficiently predict the fracture behavior of larger specimens, providing practical insights for engineering applications.

Numerical study on the anti-collision performance of recycled foam concrete beam guardrail under vehicle collision

Recycled foam concrete (RFC) possessed excellent energy absorption capabilities and could be used in the anti-collision field. To address the insufficient anti-collision performance of existing guardrails, this paper presented a novel RFC beam guardrail by combining RFC with box-shaped steel shells. The quasi-static compressive tests and drop hammer impact tests were applied to analyze the static and dynamic mechanical characteristics of RFC with different densities and sand-cement ratios. Then, the vehicle collision performance of the RFC beam guardrail (RBG) and standard beam guardrail (SBG) was tested by LS-DYNA. The results showed that, compared with SBG, RBG had better guiding and energy absorption effects, reduced the peak vehicular acceleration by 44.15 % and the maximum guardrail displacement by 73.22 % during vehicle collisions, and mitigated the damage to the vehicle. Therefore, it is a viable way to utilize RFC to fabricate RBG, which could not only repurpose the construction and demolition wastes (CDW) but also acquire guardrails with enhanced anti-collision performance.

Research on the flexural capacity of corroded recycled aggregate concrete beams by finite elements method

In this paper, based on the experimental fitting method of recycled concrete beams with corroded rebar, finite element analysis by changing the values of factors affecting the flexural capacity was conducted. The results showed that the flexural capacity of recycled concrete beams increased with the increase of section width and height.

Experimental and numerical investigation of preloaded recycled concrete beams strengthened with CFRP

Purpose The use of recycled coarse aggregate in concrete structures promotes environmental sustainability; however, performance of these structures might be negatively impacted when it is used as a replacement to traditional aggregate. This paper aims to simulate recycled concrete beams strengthened with carbon fiber-reinforced polymer (CFRP), to advance the modeling and use of recycled concrete structures. Design/methodology/approach To investigate the performance of beams with recycled coarse aggregate concrete (RCAC), finite element models (FEMs) were developed to simulate 12 preloaded RCAC beams, strengthened with two CFRP strengthening schemes. Details of the modeling are provided including the material models, boundary conditions, applied loads, analysis solver, mesh analysis and computational efficiency. Findings Using FEM, a parametric study was carried out to assess the influence of CFRP thickness on the strengthening efficiency. The FEM provided results in good agreement with those from the experiments with differences and standard deviation not exceeding 11.1% and 3.1%, respectively. It was found that increasing the CFRP laminate thickness improved the load-carrying capacity of the strengthened beams. Originality/value The developed models simulate the preloading and loading up to failure with/without CFRP strengthening for the investigated beams. Moreover, the models were validated against the experimental results of 12 beams in terms of crack pattern as well as load, deflection and strain.

Effects of steel fibers on the flexural behavior of recycled concrete beam: Testing and analysis

Bending tests were conducted on beams made of steel fiber reinforced recycled aggregate concrete (SFRRAC) in this study. The investigation focused on the primary design parameters: water-cement ratio, replacement rate of recycled coarse aggregates (RCA), and steel fiber volume fraction. Based on the experimental results of 13 beams in this study and 101 SFRRAC beams from relevant published literatures, the bond coefficients of steel fibers on the recycled aggregate concrete (RAC) beams were calculated using the flexural capacity calculation methods outlined in both Chinese and American specifications for steel fiber reinforced concrete beams. The reliability of the steel fiber bond coefficients was assessed through probabilistic statistical methods, examining their probability distribution. The findings indicate that steel fibers can significantly enhance the flexural behavior of RAC beam. When applying the steel fiber bond coefficient recommended by the Chinese specification for SFRRAC beams, the flexural capacity predictions tended to be non-conservative. Conversely, the steel fiber bond coefficient recommended by American specification led to conservative estimates of flexural capacity. Drawing on the statistical analysis, a reasonable range of steel fiber bond coefficients for SFRRAC beams was proposed, which could better evaluate the flexural capacity of SFRRAC beams while ensuring safety and economy of engineering.

Study on Crack Resistance and Calculation Model of RAC Beams Strengthened with Prestressed CFRP

With the development of recycled aggregate concrete (RAC), the recovery rate of construction waste is improved, and the pollution problem is alleviated. In particular, RAC beams strengthened with prestressed carbon fiber reinforced plastics (CFRP) can exhibit improved mechanical properties, expanding RAC application. Four groups of reinforced RAC beam specimens contained 0%, 40%, 70%, and 100% recycled coarse aggregate, respectively. Each group of beams was first pre-cracked and then strengthened by prestressed CFRP with one layer and two layers respectively. Finally, the bearing capacity tests were performed for these beams. The test results show that as the recycled coarse aggregate content increases, the cracking moment and ultimate load capacity of the beam decrease, while its crack width increases. As the CFRP layer increases, the deformation and crack width of the beam decreases, while the number of cracks increases. The prestressed CFRP also exhibited tensile and peeling failure. A beam deflection calculation model was established by introducing a coefficient k representing the interaction between recycled aggregate and CFRP. The influence coefficient of concrete elongation on the crack width and average crack spacing of the beam was modified, and the crack width analysis model of the beam was established. The calculated results are in good agreement with the experimental observations. It can provide reference for the application and design of recycled concrete beams strengthened with prestressed CFRP.

Shear strength of stirrup-free recycled aggregate concrete beams reinforced with steel fibers

Shear strength of stirrup-free recycled aggregate concrete beams reinforced with steel fibers

Experimental Study on Flexural Performance of Recycled Steel Fiber Concrete Beams

We sorted the waste from mechanical processing to form recycled steel fibers. In order to study the flexural mechanical properties of reinforced concrete beams after the addition of recycled steel fibers, four recycled steel fiber concrete beams (RSFCBs) and one normal concrete beam (NCB) were designed and poured using the volume fraction of steel fibers (0%, 0.5%, 1%, 1.5%, 2%) as the variables. Normal section bending tests were conducted on them under a concentrated load. We obtained experimental data such as the cracking load, ultimate load, mid-span deflection, and steel and concrete strain of the beam by gradually loading the test beam, and we observed and recorded the development of cracks. The results indicate that the NCB exhibits crushing failure, while the RSFCBs exhibit equilibrium failure. The addition of recycled steel fibers effectively controls the extension of cracks, resulting in a better bending toughness of the beam. The bending performance of RSFCBs with different volume additions shows a trend of first increasing and then decreasing with the increase in steel fiber content. The peak value was reached when the steel fiber content was 1.5%, which increased the bending bearing capacity by 54.72% compared with the NCB. With the increase in steel fiber content, the required load value for tensile steel bars to yield also increases, reaching a peak at a content of 1.5%, which increases the bending bearing capacity by 44.64% compared with the NCB. The addition of recycled steel fibers enables the beam to improve its bearing capacity while limiting the development of longitudinal reinforcement strain, allowing the longitudinal reinforcement to yield under higher loads and improving the overall bending performance of the beam.

Behavior of reinforced recycled aggregate concrete beams and slabs strengthened in flexure and punching with CFRP composites

Recycling of concrete generated from construction and demolition waste as coarse aggregates in concrete has been a focus of several studies for the evolution of the green concrete and conservation of natural resources. This investigation, therefore, focusses on the study of the behavior of RC beams strengthened with externally bonded CFRP wraps, cast with both natural and recycled aggregates concrete. Furthermore, one-way slabs were strengthened with Near Surface Mounted (NSM) bars, while two-way slabs were strengthened with CFRP strips. One-way and two-way slabs used in the study were cast with both natural and recycled aggregate concrete (RAC). In RAC, natural aggregates were replaced by 30% recycled concrete aggregates. All beams and slabs were cast with concrete mix design of 1:1.24:2.6 and w/c ratio of 0.43. Beams and one-way slabs, control and strengthened, were tested under four-point bending. Whereas, two-way slabs were tested in punching. A significant increase in the load-carrying capacity was observed for both natural and recycled aggregates concrete beams without shear reinforcement and two-way slabs, indicating the effectiveness of strengthening scheme. Increase of 20.5% and 12.6%, respectively, was found in the load-carrying capacities for the cases of both and natural and RAC beams with natural aggregate concrete (NAC) and RAC beams when results were compared for the case of shear deficient control and strengthened RC beams with CFRP wraps. Furthermore, increase of 27 − 37% was noted in load-carrying capacities of both natural and RAC two-way slabs when results were compared for the case of control and strengthened NAC and RAC slabs.

Shear strength of recycled aggregate concrete beams without shear reinforcement

Steel fibers have recently become increasingly popular for strengthening reinforced concrete members. This research contains a study of shear strength under the effect of replacing 50% of natural coarse aggregate (gravel) with recycled aggregate (crushed brick) as well as the effect of steel fibers for natural aggregate concrete and recycled aggregate concrete. Five concrete beams with dimensions of 2000 mm in length, 300 mm in depth, and 200 mm in width were tested to evaluate the effect of recycled aggregates and to evaluate the efficiency of steel fibers in improving the shear capabilities of concrete beams. Beams are designed to fail due to shear stresses (without shear strengthening). The specimens were reinforced with four 4" X 16" steel bars at the bottom and two 2" X 10" steel bars as top reinforcement. Three volumetric fractions of steel fibers were used: 0%, 0.5%, and 1%. The samples were subjected to a two-point loading test. The beam samples have a ratio of shear span to effective depth (a/d) equal to 2. The results showed that replacing 50% of natural aggregate with recycled aggregate decreased ultimate shear strength, but adding steel fibers by 1% by volume resulted in an increase of 31.8% in shear strength for a recycled concrete beam. For ordinary concrete, the final shear strength increased by 18.3% and 30.8% when steel fibers were added by 0.5% and 1%, respectively. Moreover, the results also showed that the failure mode of all samples is the shear failure mode.

Retracted: Electrochemical Preparation of Recycled Self-Compacting Concrete Composite Beams and Their Application in Prefabricated Buildings

Retracted: Electrochemical Preparation of Recycled Self-Compacting Concrete Composite Beams and Their Application in Prefabricated Buildings

Effect of hybrid fibers on the flexural performance of high‐strength recycled aggregate concrete beams

AbstractFibers are mixed within reinforced high‐strength recycled aggregate concrete (RHRAC) beams to improve their flexural performance. This study experimentally and analytically investigates the effect of using RAC combined with polyvinyl alcohol fiber (PVAF) and steel fiber (SF) on the flexural performance of RHRAC beams. A total of 11 RHRAC beams (150 × 300 × 2600 mm3) are manufactured and subject to four‐point flexural testing. The parameters of the concrete are investigated, including the volume content of the PVAF and SF. The experimental results show that SF increases the flexural strength of RHRAC beams more than PVAF does. Conversely, the effect of PVAF on deformability is more significant than that of SF. In addition, the positive influences of hybrid fiber (PVAF and SF) on the crack load, flexural capacity, and deformation capacity are superior to those of single‐mixed PVAF or SF. Three different specifications are used to calculate the flexural capacity of the test beams, among which, JGJ/T465‐2019 is the most reliable.

Analysis of the shear behavior of reinforced recycled aggregate concrete beams based on shear transfer mechanisms

This study aims to contribute to a more rational understanding of the shear behavior of reinforced recycled (concrete) aggregate concrete beams. Twelve reinforced concrete beams - six with natural aggregate concrete (NAC) and six with 100% coarse recycled concrete aggregates (RAC) - with same concrete compressive strength (38 MPa) and proportions of cement and aggregates per volume, varying the longitudinal (1.15%, 1.75%, and 2.50%) and transverse (0%, 0.086%, and 0.114%) reinforcement ratios, were tested under a 4-point bending setup with a full-field displacement monitoring. A thorough examination of the failure span along the tests, associating critical crack shape and kinematics with an investigation of the shear transfer mechanisms provided by mechanical models from the literature was conducted. Direct shear tests on push-off specimens followed by analyses of their failure surface evaluated the characteristics of shear crack surfaces and a proper modeling of the aggregate interlock contribution. The results showed a 28% average reduction in the shear strength of RAC beams with no stirrups in comparison with their reference beams (NAC), whereas beams with stirrups of same characteristics showed a similar shear strength, regardless of the type of coarse aggregate. The evaluation of the shear transfer mechanisms enabled an understanding of the reasons for those behaviors. Experimental results were also compared with those predicted in design codes. They were conservative for beams with stirrups, and, in general, less accurate than those obtained by the shear transfer mechanisms.

Evaluation of shear behavior of prepared recycled concrete aggregate concrete deep beam

Evaluation of shear behavior of prepared recycled concrete aggregate concrete deep beam

Flexural performance of recycled concrete beam reinforced with modified basalt fiber and nano-silica

To increase the surface roughness of basalt fiber (BF) and enhance the bonding properties with the concrete matrix, three modified solutions were prepared to treat the BF surface. The BF surface was modified by the best mixture-ratio solution after SEM and AFM tests. Modified basalt fiber (MBF) and nano-silica (NS) were used as reinforcing materials to improve the RC. The MBF and NS contents were used as the mix ratio control parameter. Ten recycled concrete beams were designed. Through a four-point flexural test, the destruction characteristics, deflection, cracking load, maximum bearing capacity, and strain of RC beams were obtained. The effects of replacement rate, MBF content, and NS content on the flexural properties of the RC beams were obtained. The results showed that in comparison to modification by other solutions, the surface roughness of BF was greater with modification by 2.91% KH550 and 5% NS mixed solution. The failure characteristics were similar for natural aggregate concrete beams and RC beams reinforced with MBF and NS; all underwent four stages of ordinary concrete damage. The natural aggregate concrete beams had greater flexural strength and flexural resistance than RC beams. However, the MBF and NS, added separately or together, improved the dehiscence load, peak load, ductility, and tensile strain of the RC beams. The current standards can be used to calculate the cracking moment and ultimate bearing capacity of MBF and NS reinforced RC beams; their effect was significant.

Recycled concrete beams subjected to combined reinforcement corrosion and static pre-loading

To investigate the flexural behavioural characteristics of recycled concrete beams under the combined action of steel corrosion and static pre-loading, 12 recycled concrete beam specimens, encompassing a combination of three recycled coarse aggregate (RCA) replacement ratios (0, 50 and 100%) and four static pre-load levels expressed as ratio of the ultimate moment capacity (0, 0.2, 0.4 and 0.6), were prepared for accelerated corrosion test and four-point bending test. The test results indicated that under a given RCA replacement ratio of the beams, the maximum width of corrosion-induced longitudinal cracks exhibited a linear relationship with the corresponding corrosion depth of longitudinal tension reinforcement. For the beams with 50% RCA replacement ratio, when the applied static pre-load level increased from 0 to 0.6, the ultimate load and ultimate deflection reduced by 10.4% and 21.2%, respectively, whereas for the beams with 100% RCA replacement ratio, the corresponding reduction in ultimate load and ultimate deflection were respectively 8.9% and 35.5%. Theoretical degradation models for the ultimate moment capacity and yield moment capacity of corroded beams were proposed, whereby the analytical values were in good agreement with the experimental values. This study provides useful reference for practical analysis of recycled concrete beams, which promote sustainable concrete construction.

Calculation on flexural capacity of recycled aggregate concrete beams

Based on the constitutive relation of recycled aggregate concrete (RAC, referred to as recycled concrete), from the calculation formulas of the equivalent rectangular block parameters in the compression zone of recycled concrete beams under different recycled coarse aggregate replacement ratios, the calculation formulas of the key parameters 𝛼1 and 𝛽1 of recycled concrete are deduced. Based on 𝛼1 and 𝛽1, the flexural bearing capacity of recycled concrete beams is given. In addition, the nonlinear finite element method is applied, and the simulation results are compared with the calculation results to verify the accuracy of the calculation results. Then, the limit compression zone height and maximum reinforcement ratio of recycled concrete beams, as well as the variation characters of compression zone height and reinforcement ratio under certain size and load are analyzed and obtained.

Calculation of shear capacity of recycled concrete beams with web reinforcement based on modified compression field theory

Based on the modified compression field theory, this paper considers the inter-locking force between recycled concrete aggregates and their effective grain sizes, and establishes a shear model to describe accurately the actual force of recycled concrete beams with web reinforcement. Mathematical formulas for calculation of the interlocking force are deduced, and the shear capacity of the recycled concrete beams can be estimated. The data of five test beams and 20 test beams in open literature are in good agreement with the theoretical prediction, which proves that this method can be used to calculate the ultimate shear capacity for practical applications.

Shear Strength of Concrete Beams without Stirrups Made with Recycled Coarse Aggregate

Eco-friendly concrete that considers waste material and requires less energy for production is in demand because it produces less carbon dioxide, reduces the consumption of raw material, and can be a cheaper option to conventional concrete. The objectives of this study are to investigate the shear behavior of reinforced concrete beams made with locally produced recycled coarse aggregate from construction demolition waste, study the important parameters that affect the shear strength and ductility, and check the applicability of the available theoretical shear strength predictive equations to recycled concrete. An experimental program that involved the testing of fifteen half-scale beams in shear without stirrups was carried out with a theoretical component. Results of the study showed that recycled concrete beams employing 50% recycled coarse aggregate had on average 27% lower shear strength than corresponding beams made with natural aggregate when tested at a shear span-to-depth ratio equal to 1.15, and almost the same strength as the natural aggregate beams when subjected to a shear span-to-depth ratio equal to 2.5. On the other hand, the average shear strength of beams utilizing 100% recycled aggregate was lower by 5% than the strength of their natural aggregate counterparts, irrespective of the shear span-to-depth ratio. The longitudinal steel reinforcement ratio had less effect on the shear strength provided by recycled concrete beams than on those made with natural aggregate, possibly due to the reduced ability of such concrete to develop strong dowel action. Although the use of higher strength concrete improved the shear strength of recycled aggregate beams, there was no clear correlation between the square-root of the concrete compressive strength and the shear strength provided by the concrete. The theoretical part of the study showed that the ACI 318 code and the strut-and-tie method can be reliably used to predict the shear strength of concrete made with recycled coarse aggregate employed in shallow and deep beams, respectively.

Deep learning shear capacity prediction of fibrous recycled aggregate concrete beams strengthened by side carbon fiber-reinforced polymer sheets

The goal of this paper is to evaluate the shear capacity of fibrous recycled aggregate concrete beams side bonded with carbon fiber-reinforced polymer (CFRP) based on numerical modeling and deep learning. Forty-five models were numerically investigated in ANSYS with different lengths and layers of vertical CFRP sheets. Concrete properties built for coarse recycled aggregate and various fibers as 3D and 5D steel, synthetic, and hybrid fibers added at a 0.75% volume fraction. Finally, feedforward, cascade-forward backpropagation, and NARX network algorithms were adopted to predict the shear capacity. Shear capacity improvement was significantly affected by CFRP rehabilitation. Double-layered rehabilitation applied on the zone between support and load was the most adequate. The performance of cascade-forward backpropagation in the estimation of shear capacity was superior to the other deep autoencoder models. The present paper offers good guidance on the practice field as a valuable supplement to the laboratory investigation and theoretical calculations.